---do you play basketball every day?--Half an hour.A. WhenB. WhatC. WhoD. How long

问题补充：

---do you play basketball every day?

----Half an hour.

A. When

B. What

C. Who

D. How long

答案：

A. When

B. What

C. Who

(答案→)D. How long

解析：根据答语的内容Half an hour.，可知道提问的句子意思应该为多久，即文多长时间，故选答案为D